During pregnancy, you may find your baby's appearance just as interesting as his internal development. Later in pregnancy, you may be able to see a significant amount of your baby's external development during an ultrasound. However, you can imagine what your baby looks like with information about his development earlier in the pregnancy.
Weeks 1 to 5
Once your baby is conceived and has implanted into your uterus, she is really just a ball of cells. The embryonic period begins around week five of pregnancy, according to MayoClinic.com, meaning that your baby is in three layers that will form into her skin, nervous system, organs and lungs. At this stage, she is 1/16 to 1/8 inch long, about the size of a tip of a pen.
Weeks 6 to 12
At six weeks gestation, your baby already has basic facial features and arches where his jaw will develop. His body is in a crescent shape and he has small buds for his arms and legs. By eight weeks, he has tiny nostrils and forming fingers and ears. His upper lip and nose are formed, and his trunk is strengthening. His eyes and nipples are also visible. By nine weeks, his arms can bend at the elbows and his toes are forming. His head grows to become more round. His neck starts to develop at 10 weeks, and his eyelids close to protect his eyes from amniotic fluid. By 12 weeks, his eyes are set wide apart, his external genitals are forming and he has basic fingernails. At the end of this period, he is 2 ½ inches long.
Weeks 13 to 20
Between weeks 13 and 14 of pregnancy, your baby develops fingerprints. Her skin is transparent, and a fine hair called lanugo is on her head. By 16 weeks, she is already 6 inches long. At 20 weeks, she has eyebrows and eyelashes, and is 8 inches long. Vernix, a white pasty substance that protects her skin from amniotic fluid, covers her body. At this age, an ultrasound technician may be able to detect her gender.
Weeks 21 to 30
At week 21, lanugo covers his entire body instead of just his head. His skin is less transparent because of the fat developing on his body, and he is 10 to 11 inches long by 23 weeks. He grows to be 14 inches long at 26 weeks. By 30 weeks, he is steadily storing fat and filling out his body.
Weeks 30 to 40
At 30 weeks of pregnancy, your baby's bones are fully developed and her eyes are wide open. Her sex organs are becoming more developed and prominent, and, by 32 weeks, her toenails are visible. Vernix becomes thicker around 35 weeks, and she begins to rapidly gain weight. Lanugo disappears and her skin becomes less red and wrinkled. She moves to the head-down position around 37 weeks, and by week 39 she has breast buds and long fingernails. She grows to be about 19 to 21 inches during this period.